Clicking on the recently opened item will open a listing of all items you have “recently” opened (it tracks a few hundred items that you were last to look at). Pretty simple
Any items that you save changes to, or comment on will show up here, once again, pretty simple
This tracks changes made by other people to items that are in your “Recently Edited” list. When you open these items they then are removed from this list (but remain in your Recently Edited list).